1. Field of Invention
The present invention relates to control devices for internal combustion engines.
2. Description of Related Art
Direct-injection compression-ignition engines, typified by diesel engines, are known in which fuel injection timing is advanced for premixed combustion in order to reduce emissions of nitrogen oxides (NOx) and particulate matter while the ignition timing is kept approximately at top dead center (TDC) of the piston so that degradation of fuel efficiency is suppressed.
However, when the fuel injection timing is advanced in a direct-injection spark-ignition engine, part of the fuel adheres to the crown surface of the piston, and burns without being vaporized. This leads to an increase in the amount of particulate matter emitted by the engine. Conversely, when the fuel injection timing is delayed, part of the fuel directly hits the wall of the cylinder bore and adheres thereto since the piston is located at a low position remote from TDC. The adhered fuel is scraped off into the oil pan by the movement of the piston, and disadvantageously dilutes the engine oil.